1. Field of the Invention
The present invention relates to a printing apparatus such as a printer or photocopier, and more particularly, to a method for adjusting the tension applied to a photoreceptor belt that circulates along a predetermined track.
2. Description of the Related Art
In printing apparatuses which are used to form a desired image on a printing paper, a latent electrostatic image is formed on a photoreceptor such as a photosensitive drum or a photoreceptor belt, and developed by a toner of a predetermined color. Then, the developed image is transferred to a printing paper.
FIG. 1 is a schematic view of major elements of a conventional printing apparatus. Referring to FIG. 1, the conventional printing apparatus includes a photoreceptor belt 10, and a driving roller 20, a backup roller 30 and a tension roller 40 which circulate the photoreceptor belt 10 along a given track.
A major charging station 50 for charging the photoreceptor belt 10 is placed over a part of the photoreceptor belt 10. A laser scanning unit (LSU) 60 for emitting a laser beam onto the photoreceptor belt 10 according to an image signal to form a latent electrostatic image thereon, and a development unit 70 for developing the latent electrostatic image with a developer containing a toner of a predetermined color and a liquid carrier, are installed below the photoreceptor belt 10. In general, color printers comprise a plurality of LSU's 60 and a plurality of development units 70 which contain different color developer.
The liquid carrier is removed from the developer which is applied to the photoreceptor belt 10 by a drying roller 81 and a heating roller 82, thereby drying the surface of the photoreceptor belt 10. As a result, a toner image is formed by the toner remains on the latent electrostatic image of the photoreceptor belt 10. The toner image is transferred onto a printing paper 93 by a transfer roller 91 which is installed parallel to the backup roller 30 while the photoreceptor belt 10 is interposed therebetween. The printing paper 93 is supplied between the transfer roller 91 and a pressure roller 92 which is installed parallel to the transfer roller 91, being separated by a predetermined distance, and the toner transferred onto the print paper 93 is heated and pressed by the pressure roller 92, so that the toner is fixed onto the printing paper 93.
Also, the printing apparatus includes a tension adjusting device 100 for adjusting the tension of the photoreceptor belt 10. The tension adjusting device 100 adjusts the tension applied to the photoreceptor belt 10 by applying pressure to the tension roller 40 or releasing pressure therefrom.
FIG. 2 is a perspective view of the tension adjusting device of FIG. 1. The tension adjusting device 10 of FIG. 2 uses a spring 142 and an eccentric cam 150.
In detail, the conventional tension adjusting device 100 includes an auxiliary frame 110 for supporting the tension roller 40 rotatably, and a fixed frame 120 fixed to a main frame 1, and a guide bar 130 for connecting the auxiliary frame 110 and the fixed frame 120.
The auxiliary frame 110 has grooves 111 to which a rotary shaft 41 of the tension roller 40 is coupled, and an elastic plate 112 which covers the installation groove 111 to press the rotary shaft 41 of the tension roller 40. The fixed frame 120 has a hole 121 at the center portion, to which the guide bar 130 is slidably inserted. The guide bar 130 is inserted into the hole 121 to be movable, and one end of the guide bar 130 is coupled to the auxiliary frame 110 by a coupling pin 113. A screw part 131 is formed at the middle portion of the guide bar 130, and is screw-coupled with a nut 141. A spring 142 is installed around the guide bar 130. The eccentric cam 150 that rotates by a driving motor 160, is installed at the other end of the guide bar 130, to control the elastic force applied to the spring 142. Also, a pressing ring 143 is slidably installed around the guide bar 130 such that it can press the spring 142 as the eccentric cam 150 rotates.
In the operation of the tension adjusting device 100 having the above structure, in a normal print mode where the printing apparatus normally operates for printing, the eccentric cam 150 presses the pressing ring 143, so that the guide bar 130 is pushed toward a direction A. Accordingly, the tension roller 40 is moved in the direction A, so that tension is applied to the photoreceptor belt 10. In the case when a worn belt needs to be replaced (referred to as belt replace mode), the pressure applied to the spring 142 is decreased by the rotation of the eccentric cam 150, so that the tension roller 40 moves in a direction B. Accordingly, the tension applied to the photoreceptor belt 10 is released.
As described above, the conventional tension adjusting device 100 is designed to adjust the tension applied to the photoreceptor belt 10 according to two modes: the normal print mode and the belt replace mode. Thus, even when the printing operation stops due to reasons other than the replacement of the photoreceptor belt 10, the tension applied to the photoreceptor belt 10 remains. Also, if the tension applied to the photoreceptor belt 10 is released by switching the normal print mode into the belt replace mode in this case, the photoreceptor belt 10 is loosened and falls down, contacting other units such as the LSU 60 (see FIG. 1) or the development unit 70 (see FIG. 1), installed below the photoreceptor belt 10, causing contamination or damage to the surface of the photoreceptor belt 10.
Meanwhile, in the case when the operation of the printing apparatus stops, if the photoreceptor belt 10 is left for a long time while tension is applied thereto, three bent portions of the photoreceptor belt 10, contacting the driving roller 20, the backup roller 30 and the tension roller 40, are partially stiffened, resulting in folds on the photoreceptor belt 10. As a result, the lifetime of the photoreceptor belt 10 becomes short. Also, such folds on the photoreceptor belt 10 distort the image developed thereon during a printing process, thereby deteriorating the quality in development.